Koch brothers to host conference near Vail, Colo.

Protesters demonstrate across the street from the Rancho Las Palmas Resort… (Katie Falkenberg / For The…)

An invitation-only conference of wealthy conservative activists organized by the billionaire brothers Charles and David Koch will convene just outside Vail, Colo., this weekend.

Common Cause -- a group that describes itself as nonpartisan and headed by a former Democratic congressman -- and ProgressNow Colorado have organized a protest outside the Ritz Carlton at Bachelor Gulch, where they believe the conference will be held.

The groups have urged their followers to arrive with signs that read, "UnVail the Kochs," "Corporations are not people," and "Stop the War on the Middle Class."

This is the second Koch-organized conference this year. The previous event, held in late January in Palm Springs, drew about 800 to 1,000 protesters who rallied against the Kochs' libertarian agenda. About 25 protesters were arrested for trespassing.

The Kochs have been a target of liberal activists for their funding of research institutions and other groups that push a limited-government agenda. They control Koch Industries, an energy conglomerate that is the nation's second-largest privately held company. They are credited with helping to organize the "tea party" and allied groups that spent millions to defeat Democrats in last year's midterm elections.

"We're talking hundreds of millions of dollars," said Kjersten Forseth, executive director at ProgressNow Colorado. "They're getting direct corporate profits that they're able to use for funding these organizations."

A Koch spokesman would not comment about the Vail event and would not say who would be attending. The Richmond Times-Dispatch reports that Virginia Gov. Bob McDonnell will attend.

In the past, attendees have included GOP leaders and commentator Glenn Beck. House Republican leader Eric Cantor of Virginia attended the Palm Springs event in January.

Koch spokeswoman Nancy Pfotenhauer, in an interview in Palm Springs in January, said the event, "brings together some of America’s greatest philanthropists and job creators…who share a common belief that the current level of government spending in our nation is simply unsustainable.”